Abstract/Summary

We present a novel kinetic multi-layer model that explicitly resolves mass transport
and chemical reaction at the surface and in the bulk of aerosol particles (KM-SUB).
The model is based on the PRA framework of gas–particle interactions (P¨oschl et al.,
5 2007), and it includes reversible adsorption, surface reactions and surface-bulk exchange
as well as bulk diffusion and reaction. Unlike earlier models, KM-SUB does
not require simplifying assumptions about steady-state conditions and radial mixing.
The temporal evolution and concentration profiles of volatile and non-volatile species
at the gas-particle interface and in the particle bulk can be modeled along with surface
10 concentrations and gas uptake coefficients.
In this study we explore and exemplify the effects of bulk diffusion on the rate of reactive
gas uptake for a simple reference system, the ozonolysis of oleic acid particles,
in comparison to experimental data and earlier model studies. We demonstrate how
KM-SUB can be used to interpret and analyze experimental data from laboratory stud15
ies, and how the results can be extrapolated to atmospheric conditions. In particular,
we show how interfacial transport and bulk transport, i.e., surface accommodation, bulk
accommodation and bulk diffusion, influence the kinetics of the chemical reaction. Sensitivity
studies suggest that in fine air particulate matter oleic acid and compounds with
similar reactivity against ozone (C=C double bonds) can reach chemical lifetimes of
20 multiple hours only if they are embedded in a (semi-)solid matrix with very low diffusion
coefficients (10−10 cm2 s−1).
Depending on the complexity of the investigated system, unlimited numbers of
volatile and non-volatile species and chemical reactions can be flexibly added and
treated with KM-SUB. We propose and intend to pursue the application of KM-SUB
25 as a basis for the development of a detailed master mechanism of aerosol chemistry
as well as for the derivation of simplified but realistic parameterizations for large-scale
atmospheric and climate models.